The present invention relates to means for connecting brake lines to an anti-lock braking unit, or “hydraulic unit”, of an anti-lock braking system. The hydraulic unit includes at least one pump driven by a motor, inlet and outlet valves for controlling the flow of hydraulic fluid to and from the wheel cylinders of the brakes, and at least one accumulator for storing hydraulic fluid relieved from the wheel cylinder under anti-lock action (when the ABS system intervenes to relieve braking force by relieving hydraulic fluid from one or more wheel cylinders back to the hydraulic unit). A controller is provided to monitor vehicle conditions, such as relative wheel speeds, and to control the state of the valves in the hydraulic unit and the operation of the pump. The pump returns hydraulic fluid from the hydraulic unit back to the master cylinder, which is coupled with a user-operated actuator (e.g., pedal or hand lever) to deliver hydraulic fluid to enact braking.
The hydraulic connections between the ABS hydraulic unit and both the master cylinder and the wheel cylinders of the vehicle brakes are typically made by coupling brake lines to ports on the ABS hydraulic unit with so-called “banjo” fittings. The term banjo fitting refers to the combination of a hollow bolt and a banjo block used together as described below. Near the head, the bolt includes a transverse aperture connecting with the hollow portion. The banjo block includes an opening to receive the hollow bolt, the opening having an internal chamber for establishing fluid communication with the transverse aperture in the bolt. A transverse aperture in the banjo block is provided in fluid communication with the chamber and extends away from the chamber for connection with a brake line. Most often, the outside of the banjo block is round at the bolt-receiving aperture, and the transverse aperture is arranged at a 90 degree angle with respect to the axis of the bolt-receiving aperture (thus, the resemblance to a banjo musical instrument). However, banjo blocks need not have this exact shape or orientation. Examples of the standard banjo fitting and more recent adaptations are described and illustrated in U.S. Pat. No. 7,226,088, the entire contents of which are hereby incorporated by reference.
The specific internal arrangement of valves, pump(s), and accumulator(s) within the hydraulic unit of the ABS system demands that each external port of the hydraulic unit be coupled with the brake line leading to a specific location to ensure proper operation of the anti-lock braking system. In other words, each remote component of the braking system that is fluidly coupled to the hydraulic unit has its own predetermined port on the hydraulic unit that must be utilized.
Known methods of assisting proper assembly of the brake lines to the corresponding ports on the ABS hydraulic unit include the use of fingers on round banjo blocks, controlling the routing of each brake line to a particular location, and also the use of labels or tags on the brake lines. An example of a prior art assembly aid is shown in FIG. 9. The ABS hydraulic unit 920 includes a block 924, and four brake lines 932A-D are coupled to four ports on a surface 948 of the block 924 via four banjo fittings 936A-D. Each banjo fitting 936A-D includes a hollow bolt 937A-D and a banjo block 938A-D. Two of the brake lines 932A, 932B are routed to approach the surface 948 from one side, and the other two brake lines 932C, 932D are routed to approach the surface 948 from the opposite side. Furthermore, two of the banjo blocks 938A, 938D are provided with projections in the form of bent fingers 941 that are configured to be received within positioning recesses or apertures 943 in the surface 948 of the block 924 when the banjo fittings 936A-D are properly assembled with the block 924. The fingers 941 on the banjo blocks 938A, 938D are provided to inhibit the likelihood of misassembling the set of banjo fittings 936A-D (i.e., the user can easily recognize which of the two brake lines 932A, 932B approaching from the first side should be coupled to which of the two ports on that side, and can easily recognize which of the two brake lines 932C, 932D approaching from the second side should be coupled to which of the two ports on that side). However, brake lines and fingers can be bent to different orientations, and labels can be ignored, damaged, or lost. Thus, the methods described above serve as useful aids, but provide no guarantee against improper final assembly.
U.S. Pat. No. 6,886,866 discloses a set of tube nuts of different lengths for connecting tubes to a hydraulic manifold. Tube nut stops provided on the manifold prevent misassembly of a short tube nut to the port where a long tube nut should be coupled. However, this approach requires the addition of tube nut stops to the hydraulic manifold, and it requires a large amount of free space be made available on the side of the manifold for the relatively large protrusion of the long tube nuts and tube nut stops. Furthermore, assembly of long tube nuts into the ports where short tube nuts are desired is passively discouraged (by its awkward appearance when assembled), but it is not actually prevented.